This invention relates to an improved circular saw blade for longitudinally sawing wood.
We are aware of the prior art patents to Strobel U.S. Pat. Nos. 3,563,286 and 3,700,016, relating to circular saw blades having a pair of exteriorly located, inwardly extending, non-radial slots. Our invention is an improvement on this type of circular saw blade.
The slots in the patented saw blade are intended to relieve stress, to aid in cleaning out the kerf, to attain straighter cutting action and to achieve other beneficial results. The problems which these slots are intended to solve increase with increases in diameter and decreases in thickness of a saw blade.
In each of the above patents, the trailing edge of each slot carries a hard cutting element extending substantially full length of the edge and welded or brazed full length to such edge.
We have noticed that saws having a full length or unitary cutting element per slot tend to have a relatively short life or tend, quite soon, to become damaged during operation. The former situation means frequent saw replacement, while the latter means frequent saw maintenance. We believe that the provision of a full length or unitary cutting element sets up static stresses in the saw blade, and causes dynamic stresses during the operation of the blade, and that these stresses are responsible for the problems just referred to.
Static stresses are set up because the coefficient of thermal expansion of the cutting elements is different from that of the body of the saw blade, so that when the unitary or full length cutting element is welded or brazed in place, stresses are set up in both the cutting element and in the body of the saw blade during cooling of the blade. These remain in the blade so that during operation, fracture of the cutting element and the saw blade more readily occur.
Furthermore, in the step of securing a full length unitary cutting element in place, there is a sufficient build up of heat in order to properly secure the unitary cutting element in place, that there unavoidably occurs an annealing action on the body of the blade, which is undesirable and also prevents the blade from retaining proper tension.
Dynamically, when the saw operates under binding conditions, problems arise because the unitary cutting element is relatively rigid and cannot flex and thus rubs harshly against the sides of the kerf resulting in overheating of the saw blade, causing excessive stresses in the cutting element and blade.
In addition, a saw having a full length or unitary cutting element tends to encounter certain difficulties in operation apart from the ones mentioned above. For instance, such a unitary cutting element has a difficult time breaking up collected dust in a kerf, and is adversely affected by vibration because it cannot adapt sufficiently, and thus soon breaks.
An object of the present invention is to provide a circular saw blade overcoming entirely or at least in a substantial way the above drawbacks.